1. Field of the invention
The present invention relates to a field of solid state current sources.
2. Related Application
The present application is related to a copending U.S. patent application Ser. No. 005,941, filed Jan. 22, 1984, entitled "Current Controlled Solid State Switch" and is incorporated herein by reference to provide a teaching of operating conditions encountered by MOS transistors and examples of certain applications.
3. Prior Art
In the design of solid state circuits and devices utilizing MOS technology, a stable current source is a necessary requirement in many applications. For a current source to be ideal, it must be independent of operating condition variations, such as changes in temperature, supply voltage, device parameter variations and etc. Although complex circuits can be designed to provide such a stable current source, economics or physical constraints may present prohibitive constraints.
A typical MOS transistor operating in the saturation region is a simple form of a current source. However, a transistor is susceptible to operating condition changes, including its own process variations. These changes will result in the transistor sourcing higher current as temperature decreases, supply voltage increases or process variations causing the transistor to operate in the higher saturation current region. The problem is compounded when all extreme conditions occur simultaneously.
It is appreciated that what is needed is a simply designed current source which is compensated to provide a stable and desired output even as operating conditions change.